This disclosure relates to bonded structures employing diffusion barrier structures derived from a metallic dopant element and methods of manufacturing the same.
Bonding of multiple substrates is required to enable three-dimensional integration of chips. Bonding of two substrates can be achieved by adhesion of two dielectric materials as in an oxide-to-oxide bonding that fuses silicon dioxide materials from two substrates during or after bonding, by adhesion between two metallic materials as in a copper-to-copper bonding that employs direct contact between opposing copper pads and a simultaneous or subsequent grain growth across the original interface between the opposing copper pads, or by a method employing a combination of the two adhesion mechanisms.
Lateral overlay variations during bonding of two substrates as well as vertical height variations of metal pads with respect to surrounding dielectric material layers can lead to contacts between metal pads and oxygen-permeable surfaces (such as silicon oxide surfaces) or physical exposure of peripheral surfaces of metal pads to an inter-substrate cavity. Such configurations provide path for copper migration/diffusion, and ingress path for oxygen or moisture into the metal pads and metal interconnect structures connected thereto, thereby degrading the reliability of the bonded structures.